Conventionally, an electronic circuit apparatus for controlling an engine, etc. for an automobile, is formed in such a manner that electronic parts are mounted and wired within a case forming a partition molded together with input and output terminals on a metal substrate made of aluminum etc., and the case if case is fixed by a resin cover from the underside thereof using bonding material etc. for sealing the electronic circuit apparatus as disclosed, for instance, on FIGS. 1 and 2 of Japanese patent Laid-Open No. 59-208800 published on Nov. 27, 1984 in the title of "Electronic Apparatus of Automobile".
Further, a sealing structure of an electronic circuit apparatus is disclosed, for instance, in FIG. 3 of Japanese Patent Laid-Open No. 60-213095 published on Oct. 25, 1985, and entitled "Electronic Circuit Apparatus", in which a recessed portion is provided on an upper surface of an outer wall of a metal case in which electronic parts are encased in a resin, a metal cover is engaged to the recessed portion of the flange of the metal case, and after that the thermosetting resin is cured in the recessed portion.
However, in the former structure, when the electronic circuit apparatus is used under the condition in which a difference of thermal expansion coefficients between the resin partition and the metal substrate is large, slight peeling occurs between the bonded interfaces. And there is such a problem that the peeling will spread and salt water will be introduced into the peeled interfaces, when salt is spread on a surface of the road in winter, with the result that the salt water is introduced into the peeled interfaces, and the salt is crystallized at the peeled interfaces.
In the latter prior art, it is proposed that a high density and hard epoxy resin, in which the thermal expansion coefficient thereof is nearly equal to the metal, is used as the thermosetting resin for bonding the case and the cover in order to solve the above-mentioned problem. However, the thermosetting resin can not be applied to the metal substrate and the resin partition. Namely, when the sealing structure of the latter is applied to the metal substrate and the resin partition for connecting both, peeling occurs at the bonded interface of the thermosetting resin and the metal based on the difference of the thermal expansion coefficients therebetween. Further, when the salt water is splashed on the electronic circuit apparatus, the salt water is adhered to the interval between the case and the cover, the adhered salt water is crystallized therein, and the connection among the case, the cover, and the bonding material is broken by the force which is activated to peel the resin and the bonding material. Particularly, when a gap between the case and the cover is small, the sealing is remarkably destroyed by the salt water.